From f6351b48135cb886ba6bfc4e859b5382b9bcc607 Mon Sep 17 00:00:00 2001
From: Alexandre Jesus <adbjesus@gmail.com>
Date: Wed, 24 Jan 2024 16:16:01 +0000
Subject: day18

---
 day18.lisp | 63 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 63 insertions(+)
 create mode 100644 day18.lisp

(limited to 'day18.lisp')

diff --git a/day18.lisp b/day18.lisp
new file mode 100644
index 0000000..0b35af2
--- /dev/null
+++ b/day18.lisp
@@ -0,0 +1,63 @@
+(defun read-lines (filespec)
+  (with-open-file (stream filespec)
+    (loop for line = (read-line stream nil)
+          while line
+          collect line)))
+
+(defun split-by-char (char string)
+  (loop for i = 0 then (1+ j)
+        as j = (position char string :start i)
+        collect (subseq string i j)
+        while j))
+
+(defun compute-area (moves)
+  (let* ((coords '((0 . 0)))
+         (interior 0)
+         (bound 0 ))
+    (loop for m in moves
+          as dir = (car m)
+          as len = (cdr m)
+          as prv = (car coords)
+          as prvi = (car prv)
+          as prvj = (cdr prv)
+          as curi = (cond ((equal dir #\U) (- prvi len))
+                          ((equal dir #\D) (+ prvi len))
+                          (t prvi))
+          as curj = (cond ((equal dir #\L) (- prvj len))
+                          ((equal dir #\R) (+ prvj len))
+                          (t prvj))
+          as cur = (cons curi curj)
+          do (setf coords (cons cur coords)
+                   interior (+ interior (- (* prvi curj) (* prvj curi)))
+                   bound (+ bound (abs (+ (- curi prvi) (- curj prvj))))))
+    (1+ (ash (+ (abs interior) bound) -1))))
+
+(defun get-move (line)
+  (let ((aux (split-by-char #\Space line)))
+    (cons (aref (car aux) 0) (parse-integer (cadr aux)))))
+
+(defun get-moves (lines)
+  (mapcar #'get-move lines))
+
+(defun solve1 (filespec)
+  (let* ((lines (read-lines filespec))
+         (moves (get-moves lines)))
+    (compute-area moves)))
+
+(defun get-swapped-move (line)
+  (let* ((aux (caddr (split-by-char #\Space line)))
+         (aux (parse-integer aux :start 2 :radix 16 :junk-allowed t)))
+    (cons (aref "RDLU" (mod aux 16)) (ash aux -4))))
+  
+(defun get-swapped-moves (lines)
+  (mapcar #'get-swapped-move lines))
+
+(defun solve2 (filespec)
+  (let* ((lines (read-lines filespec))
+         (moves (get-swapped-moves lines)))
+    (compute-area moves)))
+
+(print (solve1 "data/18/example.txt")) ;; 62
+(print (solve1 "data/18/input.txt"))   ;; 34329
+(print (solve2 "data/18/example.txt")) ;; 952408144115
+(print (solve2 "data/18/input.txt"))   ;; 42617947302920
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